摘要:

It is known that the diffusion of a density profile is obtained by convolving a Gaussian with the given density profile. This suggests that the time reversed process (antidiffusion) can be defined by an appropriate convolution inverse. We show that this is indeed the case and we develop a general method for calculating convolution inverses.

ISSN:0021-8979    

DOI:10.1063/1.346667

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The synchrotron x‐ray near total external fluorescence technique is used to measure the concentration profiles of elements near a sample surface along its surface normal. This novel nondestructive technique is capable of providing information about the concentration profiles on a length scale of tens to hundreds of angstroms from the sample surface. It does not require vacuum and can be applied at ambient pressures. Concentration profiles of virtually all the elements in the periodic table can be investigated using this technique. The lower limit of detection is approximately equivalent to (1)/(10) of a monolayer coverage. The technique is particularly useful in applications where the fluorescence signal originating from a thin surface layer can be normalized against that originating from the same element in the bulk of the sample. The experimental procedure and the data analysis are demonstrated using experimental results of metal‐ion segregation from a liquid solution to a liquid/air interface.

ISSN:0021-8979    

DOI:10.1063/1.346668

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Fourier transform infrared attenuated total reflectance technique was used to measure the SiOH and SiH contents in the thermal oxide films grown on Si wafers. It was found that the SiOH groups in the bulk could be eliminated by annealing at 850 °C, whereas SiOH at the Si/SiO2interface could only be removed by annealing at 1000 °C. It was also found that SiOH and SiH groups were generated in the thin oxide film by &ggr;‐ray irradiation. The presence of H or H2in SiO2is necessary to explain the result.

ISSN:0021-8979    

DOI:10.1063/1.346669

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We analyze the near‐threshold behavior of a circularly symmetric distributed feedback laser by developing a coupled‐mode theory analysis for all azimuthal modes. We show that the equations that describe the low‐order azimuthal modes are, to a very good approximation, the same as those for the one‐dimensional (linear) distributed feedback laser. We examine the behavior of higher‐order azimuthal modes by numerically solving the exact coupled‐mode equations. We find that while a significant amount of mode discrimination exists among radial (longitudinal) modes, as in the one‐dimensional distributed feedback laser, there is a much smaller degree of discrimination among azimuthal modes, indicating probability of multimode operation. Despite the multimode behavior, we find that the frequency bandwidth associated with modes that do lase ought to be smaller than the spacing between Fabry‐Perot modes of a typical semiconductor laser. This laser is an excellent candidate for a surface‐emitting laser—it should have a superb quality output beam and is well‐suited for array operation.

ISSN:0021-8979    

DOI:10.1063/1.346670

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have achieved single‐mode operation in a pulsed hybrid optically pumped D2O far‐infrared laser. The active volume of the resonator was divided into two sections separated by a thin plastic foil. The larger section served as the main gain medium and the shorter section as the mode selective element. The vapor pressure in the smaller volume was either very low or alternatively about three times higher than the pressure in the main part. In both cases single‐mode operation was achieved without any reduction of the total output energy.

ISSN:0021-8979    

DOI:10.1063/1.346671

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Multibeam coupling in a Kerr medium with a finite response time is studied theoretically. Two different frequency spectra are considered. In the first case the modes are equally spaced and in the second the frequency separations are all unequal. In either case, as the beams propagate, both spectra eventually reach a saturation characterized by a cascading of energy into the lowest frequency if the Kerr constant is positive. The direction of energy transfer is reversed if the Kerr constant is negative. Representative examples are given for a multimode, equally spaced, laser source and for an unequally spaced source. For the former case, we give the optimum medium response time for conversion of a Gaussian spectra. If the frequencies are unequally spaced we present general conditions which have to be satisfied and give two examples.

ISSN:0021-8979    

DOI:10.1063/1.346672

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The high‐repetition‐rate operation of a transversely excited atmospheric CO2laser pumped by an all‐solid‐state exciter consisting of a two‐stage magnetic pulse compressor has been tested. At a repetition‐rate frequency of 1 kpps, an average laser power of 250 W was obtained. A maximum repetition rate of 1.1 kpps was limited by either the capability of the switching power supply (20 kW) or the turn‐off time of the silicon controlled rectifier used (400 &mgr;s). The energy transfer efficiency of the exciter was 75%, and the overall laser efficiency was 3.2%. By changing the amount of the available magnetic flux swing of the cores used, 30% regulation on the input energy was also achieved with a constant energy transfer efficiency of 78%.

ISSN:0021-8979    

DOI:10.1063/1.346673

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Characteristics of an optically pumped titanium vapor laser have been investigated on the 3d2 4s(4P)4p 3D01−3d3(4F)4Rs 3F2transition at 551.4 nm. An excimer laser of 14 mJ/pulse for vaporization and an N2laser of 5 mJ/pulse for optical pumping are employed. The laser output energy is measured as a function of buffer gas pressure, delay time, output mirror reflectivity, pumping laser intensity, and vaporizing laser intensity. The possibility of lasing on the other transitions is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.346674

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The performance of the XeF(C→A) laser, pumped at a rate of 290 kW/cm3with a 600‐ns electron‐beam pulse, has been improved through the optimization of the laser gas mixture and resonator output coupler reflectivity. An intrinsic efficiency of 1.1% and a specific output energy of 2 J/l have been demonstrated. A uniformly pumped region of the gain medium was selected for diagnosis in these measurements. In a separate experiment with larger diameter mirrors, a total output energy of 4 J was recorded. These are the highest specific and total output energies reported thus far for a directly electrically excited XeF(C→A) laser. The laser pulse duration was 350 ns (FWHM), and the laser bandwidth was 160 A˚. The small‐signal net gain was measured during the electron‐beam pulse at various wavelengths, and a peak gain of 0.4%/cm was observed. The sidelight fluorescence spectrum was also recorded.

ISSN:0021-8979    

DOI:10.1063/1.346675

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An electrohydrodynamic surface capillary wave theory has previously been developed for ion and droplet formation in electrically stressed conducting viscous fluids. In this paper the formalism has been used to derive the dispersion relation for the simplest model, a planar liquid‐metal ion source, which includes both gravitational and viscous effects. The calculation required the simultaneous solution of the linearized Navier–Stokes equation, the Maxwell equation, and the time‐dependent Laplace–Young stress condition. The critical field necessary for the onset of instability of the fluid surface is obtained, as well as its dependence on surface tension, viscosity, and gravity. In addition, the effects of viscosity and gravity on the growth and decay rates of particle emission are investigated. It is found that, as a function of applied field, the effects of viscosity and gravity on the dominant capillary wave mode and growth rate range from a few percent for liquid Li to about 20%–40% for liquid Ga and Au, respectively. However, for the liquid metals Li, Al, Ga, Sn, and Au viscosity dominates gravity: a factor of 3 larger for Li to more than an order of magnitude greater for the heavier liquid metals. Finally, it is found that the field above a model protrusion on the perturbed surface is significantly larger than the average field over the liquid surface.

ISSN:0021-8979    

DOI:10.1063/1.346676

出版商:AIP    

年代:1990

数据来源: AIP